The present invention relates to hydraulic fracturing operations and, more particularly, to methods of fracturing a subterranean formation using fly ash aggregates.
Hydrocarbon-producing wells are often stimulated by hydraulic fracturing operations. In hydraulic fracturing operations, a viscous fracturing fluid, which also functions as a carrier fluid, is pumped into a producing zone at a rate and pressure such that the subterranean formation breaks down and at least one fracture is formed in the zone. Typically, particulate solids, such as sand, suspended in a portion of the fracturing fluid are then deposited in the fractures. These particulate solids, commonly referred to as “proppant particulates,” serve to prevent the fractures from fully closing so that conductive channels are formed through which produced hydrocarbons can flow.
The proppant particulates used to prevent fractures from fully closing generally comprise particulate solids, such as sand, bauxite, ceramics, or nut hulls, which are deposited into fractures using traditional high proppant loading techniques. The proppant particulates and loading techniques suffer from an assortment of drawbacks that can limit the production potential of the well. The degree of success of a fracturing operation depends, at least in part, upon the resultant fracture porosity and conductivity once the fracturing operation is stopped and production is begun. Traditional fracturing operations place a large volume of proppant particulates into a fracture, and the porosity of the resultant packed, propped fracture is then at least partially related to the interconnected interstitial spaces between the abutting proppant particulates.
An alternative fracturing operation involves placing a much reduced volume of proppant in a fracture to create a high porosity fracture. As referred to herein, a “high porosity fracture” refers to a fracture that exhibits a porosity of greater than about 40%, after the fracture has closed or applied a substantial mechanical stress. In such operations, the proppant particulates within the fracture may be widely spaced but they are still sufficient to hold the fracture open and allow for production. Such operations allow for increased fracture conductivity due, at least in part, to the fact that the produced fluids may flow around widely spaced proppant particulates rather than just through the relatively small interstitial spaces in a packed proppant bed. While this fracturing concept has been investigated in the industry, the concept has not been successfully applied for a number of reasons. Among other things, loading techniques have not been developed that can appropriately place the proppant particulates so as to provide the desired fracture conductively.